1. Field of the Invention
The present invention relates to a pump drive structure of a water pump and an oil pump in a water-cooled internal combustion engine.
2. Description of Background Art
A coaxial arrangement of the drive shafts of a water pump and an oil pump in a water-cooled internal combustion engine is generally employed, for example, as set forth in JP-A-2001-280111.
The water-cooled internal combustion engine described in JP-A-2001-280111 is mounted laterally to a motorcycle with a crankshaft thereof oriented in the lateral width thereof.
A pair of balancer shafts are arranged above and below the crankshaft with a pump drive shaft being arranged further below the lower balancer shaft. In addition, a water pump is provided with the left end of the pump drive shaft serving as a water pump drive shaft and an oil pump is provided with the right end thereof serving as an oil pump drive shaft.
Power is transmitted from the crankshaft to the balancer shafts via a gear mechanism with a chain transmission mechanism being provided between the lower balancer shaft and the pump drive shaft so that power is transmitted from the lower balancer shaft to the pump drive shaft.
The drive shafts of the water pump and the oil pump are coaxial, but are spaced apart separately from the balancer shafts. Thus, the number of shafts in the internal combustion engine is large. In addition, since the chain transmission mechanism is required between the balancer shafts and the pump drive shafts, the internal combustion engine is upsized.